Dear Sister Saad,
[It appears that you are looking for help and I agree with you. You said: May be I'm not so good at coveying what I mean and have been blamed because of my lack of expression.]
For clarity of expression, you need to do a few simple things.
1. Be brief and to the point.
2. Write your post on a document. Read it twice before posting.
3. Enter the class room like a humble student without convictions.
4. Never try to be dominating or sarcastic.
This is a sincere advice from an experienced diplomat Sister. Just read it and take it to heart.